Generally in the electrolysis of copper, when the concentrations of impurities such as As, Sb, Bi, Ni or Fe in the electrolyte increase beyond certain levels, such impurities pass into the produced copper, and degrade its quality and electric power efficiency. To avoid this trouble, the practice of carrying out the electrolysis while keeping the concentrations of impurities in the electrolyte below fixed standard levels is widely observed. These standard levels vary from one refinery to another. For example, in regard to Sb, Bi or Fe, their levels are generally on the order of 0.2 to 0.5 g/liter for Sb, 0.1 to 0.3 g/liter for Bi, and 0.5 to 2 g/liter for Fe.
For the purpose of keeping the concentrations of impurities below the standard levels, the electrolyte is purified. At present, this purification of the electrolyte is generally effected by the method of purification liberator electrolysis. Since this method electrolytically collects such impurities by simultaneously effecting deposition of metals and liberation of hydrogen on the cathode, it suffers from very low electric power efficiency. Moreover, this method entails occurrence of arsine and, therefore, proves undesirable from the standpoint of the safety of the work environment. It also has a disadvantage that the metal deposit collected electrolytically as described above and containing Sb, Bi or Fe ions is further treated for recovery of copper therefrom, this method is destined to consume a very large amount of energy.
As another method for purification of the copper electrolyte, the so-called Bolidens Process (U.S. Pat. No. 3,753,877) has been reduced to practice. This method involves forced addition to the copper electrolyte of As ion which is detrimental to the electrolysis. Thus, it is not an advantageous method either economically or from the standpoint of the preservation of environment. The method for purification of the copper electrolyte by adsorptive removal of Sb and Bi ions by the use of .beta.-stannic acid which is disclosed in the specification of U.S. Pat. No. 3,696,012, a so-called Norddeutshe Process, had also been reduced to practice. This method does not readily permit continuous adsorptive removal of impurities by passage of the solution through a column packed with the .beta.-stannic acid as the adsorbent because this adsorbent is in a powdery form. It is not economical because part of the expensive .beta.-stannic acid used as the adsorbent is dissolved in the copper electrolyte and thus a substantial amount is lost. It has another disadvantage that the adsorbent cannot be easily regenerated after it has adsorbed Sb, Bi, or other ions thereon. The method for purification of the copper electrolyte by extraction with a solvent has also been proposed (G.B. Pat. No. 2,515,862). This method has not yet been reduced to practice because the solvent pollutes the electrolyte and because the extraction is not effected with high efficiency.
Recently, chelating resins have been developed for practical use and various methods have been proposed for adsorptive removal of metal ions from solutions by use of such chelating resins. Ordinary, commercially available chelating resins, however, have no ability to provide adsorptive separation of Bi, Sb, or Fe ions from the aforementioned highly concentrated sulfuric acid solution having a sulfuric acid concentration of at least 50 g/liter. These resins have been inapplicable, therefore, to the purification of solutions containing sulfuric acid in high concentrations such as copper electrolytes.
In the specifications of U.S. Pat. Nos. 4,383,104 and 4,414,183, there are disclosed phenolic chelating resins possessing groups having methylenephosphonic acid group substitutes for part or all of the hydrogen atoms of the primary or secondary alkylamino groups introduced as chelate forming groups into phenol rings and use of such chelating resins for adsorptive separation of heavy metal ions, particularly uranyl ions.